1. Field of the Invention
The present invention relates to a process for the simultaneous treatment of dust, sludge and steel slag which are generated in an ironworks, characterized by adding dust and sludge to a molten steel slag generated in the steel-manufacturing step.
2. Description of the Prior Art
Dust or sludge generated in the steel-manufacturing step in an ironworks generally contains not only iron oxide as a main component but also Zn, Pb, Cd, Cr, Ni, Cu, Mn and the like to some extent, so that the disposal thereof as an industrial waste is difficult and costs a great deal.
On the other hand, the study on the utilization as resources of steel slag generated in the steel-manufacturing step (that is, in a convertor or electric furnace) in an ironworks has been developed. However, not all of such slag has been utilized and a part thereof has been discarded as a waste, because such slag causes expansion and disintegration due to free lime, 2CaO.multidot.SiO.sub.2 and the like.
Therefore, steel slag has been modified so as not to cause expansion and disintegration. For example, a process which comprises adding one or more of modifiers such as red mud, some kind of slag, decomposed granite or slate into a molten steel slag in a proper amount to thereby modify the slag has been carried out.
However, these modifiers can not be easily mixed with molten steel slag merely by adding. Therefore, a process which comprises blowing a bubbling gas via a lance pipe into molten steel slag to circulate the slag by convention, thereby modifying the slag has also been carried out.
This process has a disadvantage in that a lance pipe for blowing a bubbling gas into molten steel slag and a means for supporting the pipe are needed.
Further, a lance pipe inserted into molten steel slag must be properly repaired or exchanged, because the inserted part of the pipe is corroded by the molten steel slag. Consequently, the above process has also other disadvantage in that additional labor and additional equipment for the repair or exchange are required.
Furthermore, the process has another disadvantage in that molten steel slag is cooled by blowing a low-temperature bubbling gas into the slag, so that the fluidity of the molten steel slag is lowered to result in insufficient modification reaction, because the reaction is endothermic.